This study will conduct a screen of immune function in children enrolled in a clinical trial on the health effects of dental amalgam conducted through the New England Research Institutes/Forsyth Dental Center Children's Amalgam Trial consortium. The contractor will collect and assay 280 blood samples from 80 participants in the NERIFT and will collect and analyze quantitative data from these samples. Specifically, the aim of this study is to determine if children receiving dental amalgams exhibit altered immunologic function. Assessment of immune function will include determination of total white blood cell count, distribution of T-cells and subsets, B-cells,a nd monocytes, functional analyses of T-cells and B-cells, and total immunoglobulin levels. Comparisons will be made between pre- and post-treatment values within individuals i each of the two arms of the NERIFT trial, as well as between individuals in the two different arms of the study. The contractor will identify 40 subjects within each of the two arms of the study for inclusion; will obtain 10 m1 blood heperanized blood samples from each prior to treatment, 5-7 days post-treatment, 6 months post- treatment, 12 months post-treatment, and 18 or 24 months post-treatment; will perform the following assays following collection of blood: total white cell count (including the number of T-cells, T-helper cells, T- suppressor cells, monocytes and b-cells), t-cell function, B-cell function, serum immunoglobulin level, and measurement of GSH levels; and will carry out data analysis.